1. Field of the Invention
The present invention relates to a plasma accelerator. More particularly, the present invention relates to an electromagnetic induced plasma accelerator.
2. Description of the Related Art
As demands on a high-speed microprocessor and a high recording density memory increase, a technique for reducing the thickness of a gate dielectric and a lateral size of a logic device are being developed to increase the number of devices that are able to be mounted on a single semiconductor chip. In particular, a technique by which a gate length of a transistor may be reduced to 35 mm or less, a thickness of a gate oxide layer may be reduced to 0.5 nm or less, and a metalization level may be increased to 6 or more, has been intensely studied. In order to embody this technique, a high-performance etch technique and a pattern transfer technique are needed during the semiconductor chip manufacturing process. Thus, an etch technique using a plasma accelerator becomes increasingly important.
FIG. 1 illustrates a cut-away bottom, perspective view schematically showing the structure of a conventional plasma accelerator. Referring to FIG. 1, the conventional accelerator includes a circular channel 22 having a closed upper end and an open lower end, an internal circular coil 16 and a plurality of external circular coils 17, 18, 18′, and 19. Each of the internal circular coil 16 and the external circular coils 17, 18, 18′, and 19 are disposed coaxially in an X-direction and parallel to an inside and an outside of the channel 22, respectively, and collectively form a magnetic field with a magnetic pole divided physically and magnetically. The accelerator additionally includes a circular anode 24 to which a gas supply pipe 25 is connected and which ionizes a gas, and a cathode 27, which is disposed on a magnetic pole at a lower end of the channel 22, that is connected to a gas supply line 29 and supplies electrons.
The external coils 17, 18, 18′, and 19 are divided into an upper coil 17, which surrounds the outside of the channel 22, and lower coils 18, 18′, and 19 having divided sections, which surround an opening of the channel 22. Upper portions of the upper coil 17 and the internal coil 16 are partitioned by a dielectric layer 23, and a magnetic field of the upper portions is shielded. Thus, a partial magnetic field across a spatial portion 20 of the channel 22 is induced only in an opening 22A. A magnetic field formed in a portion where the lower coils 18, 18′, and 19 are disposed, partially captures electrons. As a result, only positive ions can be accelerated, thus plasma having an electrically neutral characteristic cannot be accelerated by an electric field formed by the anode 24 and the cathode 27. In addition, in the above conventional accelerator, electrons are accumulated on a surface of a substrate on which ions are to be deposited, and thus, losses, such as a charge short occur there. In addition, notching occurs in a fine pattern, thereby causing an etch profile to be nonuniform.
FIG. 2 illustrates a cross-sectional view schematically showing the structure of another conventional plasma accelerator. Referring to FIG. 2, this coaxial plasma accelerator includes a circular channel 50 having a closed upper end and an open lower end, wherein plasma generated when a gas is discharged is accelerated, a cylindrical cathode 54 disposed inside the circular channel 50, a cylindrical anode 52, which is spaced apart from the cylindrical cathode 54 by a predetermined distance, and is disposed coaxially and parallel to the outside of an opening of the channel 50, a control coil 64, which controls plasma in the circular channel 50, a cathode coil 56 disposed inside the cylindrical cathode 54, an anode coil 58 disposed outside the cylindrical anode 52, and a magnetic inductor 70 that induces a magnetic field to the opening of the circular channel 50 by flowing current through the cathode and anode coils 56 and 66. A gas feed 62 and an insulator 66 are additionally illustrated.
In the above conventional accelerator, the circular channel 50 has inner and outer walls where the cylindrical cathode 54 and the cylindrical anode 52 are provided, respectively. In addition, the control coil 64 is disposed outside the circular channel 50. As such, current across the circular channel 50 is formed in the accelerator, and a magnetic field is induced in a radial direction that surrounds the cylindrical cathode 54 by the current. An example of this accelerator is a plasma accelerator mounted in a spaceship manufactured by Los Alamos National Laboratory.
The speed of the plasma ions accelerated by the accelerator represents a hypermagnetic sound velocity of about 500 eV. Thus, the plasma ions, accelerated in the circular channel 50 from the cylindrical anode 52 to the cylindrical cathode 54, are collided with the cylindrical cathode 54 such that the degree of damage to the cylindrical cathode 54 is severe and the plasma ions cannot be readily used in an etch process for a semiconductor thin-layer deposition process.